Bradley P. Ladewig

Dynamic Photo‐Switching in Metal–Organic Frameworks as a Route to Low‐Energy Carbon Dioxide Capture and Release

For post-combustion carbon dioxide capture technology to realize widespread viability, the energy costs must be drastically reduced. Current adsorbent technologies that rely on pressure, temperature, or vacuum swings consume as much as 40% of the production capacity of a power plant, most of which is associated with the liberation of CO2 from the capture medium. Ultimately this penalty, or parasitic energy load, must be brought closer to the thermodynamic minimum of about 4% to avoid prohibitive cost increases. Given that the triggers for release of adsorbed carbon dioxide, such as vacuum and heating, are so energy intensive, 3] requiring energy from the power plant, there is strong motivation to develop new release triggers that do not require extra energy from the plant, using renewable energy sources such as the sun. In conjunction with this, adsorbents with maximum gas sorption efficiency can further reduce the costs compared to the conventional energy-intensive CO2 gas separation process. Light, and in particular concentrated sunlight, is an extremely attractive stimulus for triggering CO2 release. If used with an adsorbent material that strongly absorbs sunlight concomitant with the desorption of large amounts of CO2, it may be possible to drastically reduce the energy costs. Perhaps the most attractive adsorbent candidates are metal–organic frameworks (MOFs), because of their large adsorption capacities, and the potential for incorporation of light-responsive organic groups within the pore structure. MOFs are an important class of 3D crystalline porous materials comprised of metal centers and organic ligands, joined periodically to establish a crystalline porous array. The large internal surface areas can be used to adsorb unprecedented quantities of gases, with particular interest in hydrogen, methane, 8] and carbon dioxide emergent. 7b,h,9] Methods for the incorporation of light-responsive groups within MOFs include the use of pendant groups pointing into the pores, and filling of pores with light-responsive guest molecules. The responsive groups within these materials may then alter their conformation when exposed to filtered light which results in a change in adsorption capacity, as reported thus far for static conditions. The responsive groups within these MOFs can be statically set to one position or another. For use in photoswing carbon dioxide capture, MOFs that can respond dynamically, or to the broadband radiation found in sunlight whilst loaded with adsorbed gas, are ideal. This will increase the speed of operation and lower the energy costs (see Figure 1)

Improving Adsorbent Properties of Cage-like Ordered Amine Functionalized Mesoporous Silica with Very Large Pores for Bioadsorption

In this paper, we report the successful synthesis of amine-functionalized FDU-12-type mesoporous silica with a very large pore (30.2 nm) and a highly ordered mesostructure by using 3-aminopropyltriethoxysilane (APTES) as an organosilane source. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) measurements confirmed that the materials possessed a face-centered cubic (space group Fm3m) mesostructure. Different techniques were used to obtain a significant pore and entrance size enlargement: low synthesis temperature and high hydrothermal treatment temperature. The amount of amine organosilane influenced the mesostructure of the mesoporous silica. It was found that the addition of inorganic salt (KCl) could help to maintain an ordered structure of the large pore mesoporous material. X-ray photoelectron spectroscopy (XPS), solid-state magic-angle spinning (MAS) 13C nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA) verified the incorporation of amine functional groups on the surface of the materials. The addition of amine organosilane extended the synthesis temperature domain of ordered FDU-12 materials. The amine functional group significantly enhanced the adsorption capacity of the mesoporous materials, e.g., the amine functionalized mesoporous silica had 8-fold higher bovine serum albumin (BSA) adsorption capacity than that of the unfunctionalized one. It also had 2 times higher adsorption capacity for large cellulase enzymes. The amine functional group introduced positively charged groups on the surface of the mesoporous silica, which created strong electrostatic interactions between the protein and the silica.

Post-synthetic Ti Exchanged UiO-66 Metal-Organic Frameworks that Deliver Exceptional Gas Permeability in Mixed Matrix Membranes

Gas separation membranes are one of the lowest energy technologies available for the separation of carbon dioxide from flue gas. Key to handling the immense scale of this separation is maximised membrane permeability at sufficient selectivity for CO2 over N2. For the first time it is revealed that metals can be post-synthetically exchanged in MOFs to drastically enhance gas transport performance in membranes. Ti-exchanged UiO-66 MOFs have been found to triple the gas permeability without a loss in selectivity due to several effects that include increased affinity for CO2 and stronger interactions between the polymer matrix and the Ti-MOFs. As a result, it is also shown that MOFs optimized in previous works for batch-wise adsorption applications can be applied to membranes, which have lower demands on material quantities. These membranes exhibit exceptional CO2 permeability enhancement of as much as 153% when compared to the non-exchanged UiO-66 mixed-matrix controls, which places them well above the Robeson upper bound at just a 5 wt.% loading. The fact that maximum permeability enhancement occurs at such low loadings, significantly less than the optimum for other MMMs, is a major advantage in large-scale application due to the more attainable quantities of MOF needed.

A review of reverse osmosis membrane fouling and control strategies

Reverse osmosis (RO) membrane technology is one of the most important technologies for water treatment. However, membrane fouling is an inevitable issue. Membrane fouling leads to higher operating pressure, flux decline, frequent chemical cleaning and shorter membrane life. This paper reviews membrane fouling types and fouling control strategies, with a focus on the latest developments. The fundamentals of fouling are discussed in detail, including biofouling, organic fouling, inorganic scaling and colloidal fouling. Furthermore, fouling mitigation technologies are also discussed comprehensively. Pretreatment is widely used in practice to reduce the burden for the following RO operation while real time monitoring of RO has the advantage and potential of providing support for effective and efficient cleaning. Surface modification could slow down membrane fouling by changing surface properties such as surface smoothness and hydrophilicity, while novel membrane materials and synthesis processes build a promising future for the next generation of RO membranes with big advancements in fouling resistance. Especially in this review paper, statistical analysis is conducted where appropriate to reveal the research interests in RO fouling and control.

Preparation of porous composite ion-exchange membranes for desalination application

Via a two-step phase inversion technique, composite membranes with controllable porosity and a significant improvement of electrochemical properties were successfully prepared. The presence of surface functionalized mesoporous silica (SS) as inorganic fillers in the sulfonated polyethersulfone (sPES) polymer matrix was proved to have a great impact on the resultant membrane structure, which subsequently led to significantly enhanced ionic conductivity of the membranes. The correlation among inorganic fillers, composite structures, electrochemical properties and desalination performance by electrodialysis (ED) was discussed in detail. The optimal membrane was the composite with 0.2 wt% SS loading, which possessed a good ionic conductivity of 5.554 mS cm−1, a high selectivity with 0.95 transport number while maintaining good mechanical strength and thermal stability. Moreover, the performance of this membrane in ED was comparable to a commercial membrane (FKE), exhibiting a current efficiency of 0.84 and 3.82 kW h kg−1 of salt removed.

Removal of surfactant and capping agent from Pd nanocubes (Pd-NCs) using tert-butylamine: its effect on electrochemical characteristics

Synthesis of shape-controlled nanoparticles of precious metals with defined size is well-established in the literature and the control over shape and size is achieved using surfactants and capping agents. However, a clean surface without impurities is required for realistic applications. In the present investigation, palladium nanocubes are synthesized using poly(vinylpyrrolidone) and potassium bromide. A novel method for cleaning the nanoparticle surface, i.e., treatment with tert-butylamine is reported. For comparison, a part of the untreated sample is subjected to the commonly used method of heat-treatment in an oxygen atmosphere for surface cleaning. The XPS and FTIR spectra of the heat-treated sample show incomplete removal of PVP and complete removal of Br− and the XRD pattern suggests oxide formation on the Pd surface. Treatment with tert-butylamine provides a clean surface free of PVP and Br−. Cleanliness of the surface is further confirmed by the voltammograms and ORR activities in 0.1 M HClO4. We conclude that tert-butylamine can be an effective solvent for the removal of PVP and a reagent for Br− ions because of its ability to form a quaternary ammonium salt.

The Effects of Sulfonated Poly(ether ether ketone) Ion Exchange Preparation Conditions on Membrane Properties.

A low cost cation exchange membrane to be used in a specific bioelectrochemical system has been developed using poly(ether ether ketone) (PEEK). This material is presented as an alternative to current commercial ion exchange membranes that have been primarily designed for fuel cell applications. To increase the hydrophilicity and ion transport of the PEEK material, charged groups are introduced through sulfonation. The effect of sulfonation and casting conditions on membrane performance has been systematically determined by producing a series of membranes synthesized over an array of reaction and casting conditions. Optimal reaction and casting conditions for producing SPEEK ion exchange membranes with appropriate performance characteristics have been established by this uniquely systematic experimental series. Membrane materials were characterized by ion exchange capacity, water uptake, swelling, potential difference and NMR analysis. Testing this extensive membranes series established that the most appropriate sulfonation conditions were 60 °C for 6 h. For mechanical stability and ease of handling, SPEEK membranes cast from solvent casting concentrations of 15%–25% with a resulting thickness of 30–50 µm were also found to be most suitable from the series of tested casting conditions. Drying conditions did not have any apparent impact on the measured parameters in this study. The conductivity of SPEEK membranes was found to be in the range of 10−3 S cm−1, which is suitable for use as a low cost membrane in the intended bioelectrochemical systems.

The effects of aspect ratio of inorganic fillers on the structure and property of composite ion-exchange membranes

A new type of nanocomposite ion-exchange membranes containing sulfonated polyethersulfone (sPES) polymer matrix and sulfonated surface-functionalized mesoporous silica (SS) inorganic fillers was prepared. Various characterizations revealed that the addition of inorganic fillers with different shapes had a significant influence on the membrane structure. The mesoporous inorganic fillers not only created extra pore and water channels, assisting the ionic migration and improving conductivity of the composites, but also provided additional fixed charge groups upon surface modification. This allows the Donnan exclusion to work effectively and thus improve the selectivity of membranes. It was proved that the incorporation of appropriate amount of SS additive could significantly improve the conductivity (up to 20 folds) and permselectivity (about 14%) of the sPES membranes. The performance of these newly developed membranes in desalination by electrodialysis was comparable with that of a commercial membrane (FKE).

Preparation, characterization and performance of templated silica membranes in non-osmotic desalination

In this work we investigate the potential of a polyethylene glycol-polypropylene glycol-polyethylene glycol, tri-block copolymer as a template for a hybrid carbon/silica membrane for use in the non-osmotic desalination of seawater. Silica samples were loaded with varying amounts of tri-block copolymer and calcined in a vacuum to carbonize the template and trap it within the silica matrix. The resultant xerogels were analyzed with FTIR, Thermogravimetric analysis (TGA) and N2 sorption techniques, wherein it was determined that template loadings of 10 and 20% produced silica networks with enhanced pore volumes and appropriately sized pores for desalination. Membranes were created via two different routes and tested with feed concentrations of 3, 10 and 35 ppk of NaCl at room temperature employing a transmembrane pressure drop of <1 atm. All membranes demonstrated a salt rejection capacity of >85% (in most cases >95%) and fluxes higher than 1.6 kg m−2 h−1. Furthermore, the carbonized templated membranes displayed equal or improved performance compared to similarly prepared non-templated silica membranes, with the best results of a flux of 3.7 kg m−2 h−1 with 98.5% salt rejection capacity, exceeding previous literature reports. In addition, the templated silica membranes exhibited superior hydrostability demonstrating their potential for long-term operation.

Physical aging in glassy mixed matrix membranes; tuning particle interaction for mechanically robust nanocomposite films

Despite the exceptional separation performance of modern glassy mixed matrix membranes, these materials are not being utilized to improve the performance of existing membrane technologies. Nano-sized additives can greatly enhance separation performance, and have recently been used to overcome age-related performance loss of high performance MMMs. However nano-additives also compromise the structural integrity of films and little is known on how physical aging affects their mechanical properties over time. A solution for both physical aging and mechanical instability is required before these high performance materials can be utilised in industrial membrane applications. Here, we examine physical aging in mixed matrix membranes through mechanical properties and single gas permeation measurements using three glassy polymers, Matrimid® 5218, poly-1-trimethylsilyl-1-propyne (PTMSP), and a polymer of intrinsic microporosity (PIM-1); and a range of nano-scale additives; silica, PAF-1, UiO-66, and Ti5UiO-66, each previously shown to enhance gas separation performance. We find polymer-additive interactions strongly influence local physical aging and play a key role in determining the overall material properties of glassy nanocomposite films. Strong interface interactions can slow physical aging, and may not correlate to reinforced or age-stable films. Whereas traditionally ‘incompatible’ nanocomposites exhibit mechanical properties that can improve over time and even outperform their native polymers. Tuning polymer-additive interactions is vital to achieving the physical aging, mechanical stability, and permselectivity requirements of advanced mixed matrix membrane technologies and reducing the enormous global energy cost of separation processes.